He was one of the most beloved teachers in the small world of international schools that serve the children of diplomats, well-off American expatriates and local elites. He was often the first to arrive in the morning, and the last to leave each day. He led students on class trips to exotic places, treating them to cookies and milk at bedtime.

That was the public persona of William Vahey, carefully crafted over four decades until a maid cleaning his home in Nicaragua stole a 16-gigabyte memory drive. There, in photograph after photograph, was evidence that the model teacher had molested scores of adolescent boys, possibly more, in a career spanning 10 schools on four continents.